1. Field of the Invention
The present invention relates to a scanning line interpolation equipment for interpolating scanning lines displayed by a video signal.
2. Description of the Background Art
A scanning line interpolation equipment interpolating scanning lines is employed for converting a video signal of an interlaced scanning system to a video signal of a progressive scanning system or increasing the number of scanning lines in the progressive scanning system.
Such a scanning line interpolation equipment calculates the value of a pixel (hereinafter referred to as an interpolated pixel) forming a scanning line (hereinafter referred to as an interpolated scanning line) to be created by interpolation on the basis of the values of pixels of upper and lower scanning lines.
In this case, it is proposed to calculate the value of the interpolated pixel with pixels vertically located with respect to the interpolated pixel in general and to calculate the value of the interpolated pixel with pixels obliquely located with respect to the interpolated pixel in an image having an oblique edge or an image having thin oblique lines. To this end, a correlation determination circuit determining a direction having high correlation in an image displayed by a video signal is employed.
The conventional correlation determination circuit detects the difference value between two vertical pixels and that between two oblique pixels about the interpolated pixel, for determining the angle of the direction having high correlation on the basis of the differences value. In such a method employing the difference value between two pixels, however, the angle may be falsely detected.
Therefore, it is proposed to calculate the value of the interpolated pixel with the vertically located pixels if the difference value between two pixels located in the determined direction is greater than a threshold while calculating the value of the interpolated pixel with the oblique pixels if the difference value between the two pixels located in the determined direction is less than the threshold.
In the aforementioned scanning line interpolation equipment, however, the value of the interpolated pixel is so dispersed that no smooth image can be obtained if the difference value between the two pixels located in the determined direction is approximate to the threshold.
Consider an image having an oblique edge as shown in FIG. 13, for example. It is assumed that the values of two pixels 81 and 82 located above and under an interpolated pixel IN are xe2x80x9c0xe2x80x9d and xe2x80x9c100xe2x80x9d respectively, the values of a first pair of oblique pixels 83 and 84 are xe2x80x9c0xe2x80x9d and xe2x80x9c100xe2x80x9d respectively, and the values of a second pair of oblique pixels 85 and 86 are xe2x80x9c80xe2x80x9d and xe2x80x9c120xe2x80x9d respectively. It is also assumed that a threshold is xe2x80x9c40xe2x80x9d.
In this case, the difference value between the two pixels 81 and 82 located above and under the interpolated pixel IN is xe2x80x9c100xe2x80x9d, that between the first pair of oblique pixels 83 and 84 is xe2x80x9c100xe2x80x9d and that between the second pair of oblique pixels 85 and 86 is xe2x80x9c40xe2x80x9d, and hence the direction having high correlation is along a straight line connecting the pair of pixels 85 and 86 with each other. In this case, the difference value between the pair of pixels 85 and 86 is not more than the threshold, and hence the value of the interpolated pixel IN is calculated with the oblique pair of pixels 85 and 86. For example, the average xe2x80x9c100xe2x80x9d of the pair of pixels 85 and 86 defines the value of the interpolated pixel IN.
If the value of the pixel 85 is xe2x80x9c75xe2x80x9d, however, the difference value between the pair of pixels 85 and 86 is greater than the threshold, and hence the value of the interpolated pixel IN is calculated with the two pixels 81 and 82 in the vertical direction. For example, the average xe2x80x9c50xe2x80x9d between the values of the two pixels 81 and 82 defines the value of the interpolated pixel IN.
Thus, it follows that the value of the interpolated pixel IN varies by xe2x80x9c50xe2x80x9d when the value of the pixel 85 varies merely by xe2x80x9c5xe2x80x9d. Consequently, no smooth image can be obtained.
An object of the present invention is to provide a scanning line interpolation equipment capable of smoothly interpolating an image having an oblique edge.
A scanning line interpolation equipment according to an aspect of the present invention, interpolating a scanning line by calculating the value of a pixel to be interpolated on the basis of an input video signal, comprises first interpolation means calculating a first interpolated value by interpolation employing pixels of upper and lower scanning lines vertically located with respect to the pixel to be interpolated, input means inputting a signal indicating the direction of an image with respect to the pixel to be interpolated, difference calculation means calculating the difference value between the values of pixels of upper and lower scanning lines located in the direction indicated by the signal input by the input means with respect to the pixel to be interpolated, second interpolation means calculating a second interpolated value by interpolation employing the pixels of the upper and lower scanning lines located in the direction indicated by the signal input by the input means with respect to the pixel to be interpolated and interpolated value output means outputting the second interpolated value calculated by the second interpolation means as the value of the pixel to be interpolated when the difference value calculated by the difference calculation means is not more than a first value, outputting the first interpolated value calculated by the first interpolation means as the value of the pixel to be interpolated when the difference value calculated by the difference calculation means is not less than a second value greater than the first value, and calculating a third interpolated value by an operation employing the first interpolated value calculated by the first interpolation means and the second interpolated value calculated by the second interpolation means and outputting the third interpolated value as the value of the pixel to be interpolated when the difference value calculated by the difference calculation means is within the range between the first value and the second value.
In the scanning line interpolation equipment according to this aspect of the present invention, the first interpolation means calculates the first interpolated value by the interpolation employing the pixels of the upper and lower scanning lines vertically located with respect to the pixel to be interpolated. Further, the input means inputs the signal indicating the direction of the image with respect to the pixel to be interpolated, and the difference calculation means calculates the difference value between the values of the pixels of the upper and lower scanning lines located in the direction indicated by the input signal with respect to the pixel to be interpolated. The second interpolation means calculates the second interpolated value by the interpolation employing the pixels of the upper and lower scanning lines located in the direction indicated by the input signal with respect to the pixel to be interpolated. The interpolated value output means outputs the second interpolated value as the value of the pixel to be interpolated when the difference value is not more than the first value, outputs the first interpolated value as the value of the pixel to be interpolated when the difference value is in excess of the second value greater than the first value, and calculates the third interpolated value by the operation employing the first and second interpolated values and outputs the third interpolated value as the value of the pixel to be interpolated when the difference value is within the range between the first and second values.
Thus, the value of the pixel to be interpolated is calculated by the operation employing the first interpolated value calculated with the vertical pixels and the second interpolated value calculated with oblique pixels when the difference value between the pixels obliquely located with respect to the pixel to be interpolated is between the first and second values, whereby an image having an oblique edge can be smoothly interpolated.
The interpolated value output means may add the first interpolated value calculated by the first interpolation means and the second interpolated value calculated by the second interpolation means to each other in a ratio according to the difference value calculated by the difference calculation means when the difference value is within the range between the first value and the second value, and outputs the result of addition as the value of the pixel to be interpolated.
In this case, the interpolated value output means adds the first and second interpolated values to each other in the ratio responsive to the difference value when the difference value is between the first and second values, whereby smooth interpolation is enabled.
The interpolated value output means may add the first interpolated value and the second interpolated value to each other so that the ratio of the first interpolated value calculated by the first interpolation means is increased and the ratio of the second interpolated value calculated by the second interpolation means is reduced as the difference value calculated by the difference calculation means approaches the second value from the first value.
In this case, the interpolated value output means adds the first and second interpolated values to each other so that the ratio of the first interpolated value is increased and the ratio of the second interpolated value is reduced as the difference value approaches the second value from the first value, whereby smoother interpolation is enabled.
The difference calculation means may calculate the difference values between the values of a plurality of pixels located in a plurality of directions about the direction indicated by the signal input by the input means with respect to the pixel to be interpolated respectively, and the second interpolation means may calculate a plurality of second interpolated values by interpolation employing the plurality of pixels located in the plurality of directions about the direction indicated by the signal input by the input means with respect to the pixel to be interpolated respectively, while the scanning line interpolation equipment may further comprise minimum value determination means determining the minimum value among the plurality of difference values calculated by the difference calculation means and selection means selecting a second interpolated value corresponding to the difference value determined as the minimum value by the minimum value determination means from the plurality of second interpolated values calculated by the second interpolation means and supplying the selected second interpolated value to the interpolated value output means.
In this case, the scanning line interpolation equipment calculates the difference values between the values of the plurality of pixels located in the plurality of directions about the direction indicated by the input signal with respect to the pixel to be interpolated respectively, and calculates the plurality of second interpolated values respectively by the interpolation employing the plurality of pixels located in the plurality of directions about the direction indicated by the input signal with respect to the pixel to be interpolated respectively. The scanning line interpolation equipment determines the minimum value among the plurality of difference values for selecting the second interpolated value corresponding to the difference value determined as the minimum value from the plurality of second interpolated values and supplies the same to the interpolated value output means.
Thus, false detection of the angle of the image can be corrected by determining the direction having the highest correlation among the plurality of directions and selecting the second interpolated value in the direction having the highest correlation from the second interpolated values in the plurality of directions.
The scanning line interpolation equipment may further comprise detection means detecting the values of pixels vertically located above and under the pixel to be interpolated respectively and intermediate value determination means determining whether or not the second interpolated value calculated by the second interpolation means is between the values detected by the detection means, and the interpolated value output means may output the first interpolated value calculated by the first interpolation means as the value of the pixel to be interpolated regardless of the difference value calculated by the difference calculation means when the intermediate value determination means determines that the second interpolated value is not between the values detected by the detection means.
In this case, the scanning line interpolation equipment detects the values of the pixels vertically located above and under the pixel to be interpolated respectively, and determines whether or not the second interpolated value is between the detected values. When determining that the second interpolated value is not between the detected values, the scanning line interpolation equipment outputs the first interpolated value as the value of the pixel to be interpolated regardless of the oblique difference.
Thus, the scanning line interpolation equipment can be prevented from calculating the value of the pixel to be interpolated with pixels of a false direction when falsely detecting the angle of the image, by employing not the second interpolated value but the first interpolated value if the second interpolated value is not between the pixels located above and under the pixel to be interpolated.
The scanning line interpolation equipment may further comprise vertical difference operation means calculating the difference value between pixels vertically located above and under the pixel to be interpolated, and the interpolated value output means may output the first interpolated value calculated by the first interpolation means regardless of the difference value calculated by the difference calculation means when the difference value calculated by the vertical difference operation means is less than a predetermined value.
In this case, the scanning line interpolation equipment calculates the difference value between the pixels vertically located above and under the pixel to be interpolated, and outputs the first interpolated value as the value of the pixel to be interpolated regardless of the oblique difference value when the vertical difference value is less than the predetermined value.
Thus, deterioration of picture quality resulting from false detection of the angle of the image can be prevented by employing not the second interpolated value but the first interpolated value when the vertical difference value is less than the predetermined value.
The second interpolation means may average the pixels of the upper and lower scanning lines located in the direction indicated by the signal input by the input means with respect to the pixel to be interpolated as the second interpolated value.
In this case, the second interpolated value is defined by the average of the values of the pixels obliquely located with respect to the pixel to be interpolated.
The first value may be zero, and the second value may be a preset threshold.
In this case, the scanning line interpolation equipment outputs the second interpolated value as the value of the pixel to be interpolated when the difference value is zero, outputs the first interpolated value as the value of the pixel to be interpolated when the difference value is in excess of the threshold, and outputs the third interpolated value calculated by the operation employing the first and second interpolated values as the value of the pixel to be interpolated when the difference value is within the range between zero and the threshold.
The scanning line interpolation equipment may further comprise image angle detection means detecting an image angle related to the pixel to be interpolated on the basis of the input video signal and supplying the signal indicating the direction of the image to the input means, and the image angle detection means may include binarized pattern generation means binarizing the input video signal in a predetermined detection area including a plurality of scanning lines and the pixel to be interpolated and generating a binarized pattern, reference pattern generation means generating a binary image having a plurality of directions as a plurality of reference patterns and comparison means comparing the binarized pattern generated by the binarized pattern generation means with each of the plurality of reference patterns generated by the reference pattern generation means and detecting the image angle related to the pixel to be interpolated on the basis of the result of comparison.
In the image angle detection means, the binarized pattern generation means binarizes the input video signal in the predetermined detection area and generates the binarized pattern. The reference pattern generation means generates the binary image having the plurality of directions as the plurality of reference patterns. The comparison means compares the binarized pattern with each of the plurality of reference patterns, and detects the image angle related to the pixel to be interpolated on the basis of the result of comparison.
In this case, the scanning line interpolation equipment can suppress false detection as compared with a case of employing the difference value between two pixels due to comparison of two-dimensional patterns, whereby the angle of the image having an oblique edge can be correctly detected.
When employing two-dimensional reference patterns, detected angles are not restricted to the angle of a straight line connecting pixels located on point-symmetrical positions about the pixel to be interpolated but angles therebetween can also be detected. Therefore, the angles can be detected at smaller intervals without increasing the circuit scale.
The scanning line interpolation equipment may further comprise image angle detection means detecting an image angle related to the pixel to be interpolated on the basis of the input video signal and supplying the signal indicating the direction of the image to the input means, and the image angle detection means may include maximal/minimal pattern generation means generating a maximal/minimal pattern indicating the position of the maximal point or the minimal point of horizontal luminance distribution every scanning line in a predetermined detection area including a plurality of scanning lines and the pixel to be interpolated in the input video signal, reference pattern generation means generating a plurality of reference patterns indicating the positions of the maximal points or the minimal points of horizontal luminance distribution every scanning line in the detection area and comparison means comparing the maximal/minimal pattern generated by the maximal/minimal pattern generation means with each of the plurality of reference patterns generated by the reference pattern generation means and detecting the image angle related to the pixel to be interpolated on the basis of the result of comparison.
In the image angle detection means, the maximal/minimal pattern generation means generates the maximal/minimal pattern indicating the position of the maximal point or the minimal point of the horizontal luminance distribution every scanning line in the predetermined detection area in the input video signal. Further, the reference pattern generation means generates the plurality of reference patterns indicating the maximal points or the minimal points of the horizontal luminance distribution every scanning line in the detection area. The comparison means compares the maximal/minimal pattern with each of the plurality of reference patterns, and detects the image angle related to the pixel to be interpolated on the basis of the result of comparison.
In this case, false detection is suppressed as compared with the case of employing the difference value between two pixels due to comparison of two-dimensional patterns, whereby the angle of an image having thin oblique lines can be correctly detected.
When employing two-dimensional reference patterns, detected angles are not restricted to the angle of a straight line connecting pixels located on point-symmetrical positions about the pixel to be interpolated but angles therebetween can also be detected. Therefore, the angles can be detected at smaller intervals without increasing the circuit scale.
A scanning line interpolation equipment according to another aspect of the present invention, interpolating a scanning line by calculating the value of a pixel to be interpolated on the basis of an input video signal, comprises a first interpolation device that calculates a first interpolated value by interpolation employing pixels of upper and lower scanning lines vertically located with respect to the pixel to be interpolated, an input terminal that receives a signal indicating the direction of an image with respect to the pixel to be interpolated, a difference calculation device that calculates the difference value between the values of pixels of upper and lower scanning lines located in the direction indicated by the signal received in the input terminal with respect to the pixel to be interpolated, a second interpolation device that calculates a second interpolated value by interpolation employing the pixels of the upper and lower scanning lines located in the direction indicated by the signal received in the input terminal with respect to the pixel to be interpolated and an interpolated value output device that outputs the second interpolated value calculated by the second interpolation device as the value of the pixel to be interpolated when the difference value calculated by the difference calculation device is not more than a first value, outputs the first interpolated value calculated by the first interpolation device as the value of the pixel to be interpolated when the difference value calculated by the difference calculation device is not less than a second value greater than the first value, and calculates a third interpolated value by an operation employing the first interpolated value calculated by the first interpolation device and the second interpolated value calculated by the second interpolation device and outputs the third interpolated value as the value of the pixel to be interpolated when the difference value calculated by the difference calculation device is within the range between the first value and the second value.
In the scanning line interpolation equipment according to this aspect of the present invention, the first interpolation device calculates the first interpolated value by the interpolation employing the pixels of the upper and lower scanning lines vertically located with respect to the pixel to be interpolated. The signal indicating the direction of the image with respect to the pixel to be interpolated is input in the input terminal, and the difference calculation device calculates the difference value between the values of the pixels of the upper and lower scanning lines located in the direction indicated by the input signal with respect to the pixel to be interpolated. Further, the second interpolation device calculates the second interpolated value by the interpolation employing the pixels of the upper and lower scanning lines located in the direction indicated by the input signal with respect to the pixel to be interpolated. The interpolated value output device outputs the second interpolated value as the value of the pixel to be interpolated when the difference value is not more than the first value, outputs the first interpolated value as the value of the pixel to be interpolated when the difference value is not less than the second value greater than the first value, and calculates the third interpolated value by the operation employing the first and second interpolated values and outputs the same as the value of the pixel to be interpolated when the difference value is within the range between the first and second values.
Thus, the scanning line interpolation equipment calculates the value of the pixel to be interpolated by the operation employing the first interpolated value calculated with the vertical pixels and the second interpolated value calculated with oblique pixels when the difference value between the pixels obliquely located with respect to the pixel to be interpolated is between the first and second values, whereby an image having an oblique edge can be smoothly interpolated.
The interpolated value output device may add the first interpolated value calculated by the first interpolation device and the second interpolated value calculated by the second interpolation device to each other in a ratio according to the difference value calculated by the difference calculation device when the difference value is within the range between the first value and the second value, and outputs the result of addition as the value of the pixel to be interpolated.
In this case, the scanning line interpolation equipment adds the first and second interpolated values to each other in the ratio responsive to the difference value when the difference value is between the first and second values, whereby smooth interpolation is enabled.
The interpolated value output device may add the first interpolated value and the second interpolated value to each other so that the ratio of the first interpolated value calculated by the first interpolation device is increased and the ratio of the second interpolated value calculated by the second interpolation device is reduced as the difference value calculated by the difference calculation device approaches the second value from the first value.
In this case, the interpolated value output device adds the first and second interpolated values to each other so that the ratio of the first interpolated value is increased and the ratio of the second interpolated value is reduced as the difference value approaches the second value from the first value, whereby smoother interpolation is enabled.
The difference calculation device may calculate the difference values between the values of a plurality of pixels located in a plurality of directions about the direction indicated by the signal received in the input terminal with respect to the pixel to be interpolated respectively and the second interpolation device may calculate a plurality of second interpolated values by interpolation employing the plurality of pixels located in the plurality of directions about the direction indicated by the signal received in the input terminal with respect to the pixel to be interpolated respectively, while the scanning line interpolation equipment may further comprise a minimum value determination device that determines the minimum value among the plurality of difference values calculated by the difference calculation device and a selection device that selectes a second interpolated value corresponding to the difference value determined as the minimum value by the minimum value determination device from the plurality of second interpolated values calculated by the second interpolation device and supplies the selected second interpolated value to the interpolated value output device.
In this case, the scanning line interpolation equipment calculates the difference values between the plurality of pixels located in the plurality of directions about the direction indicated by the input signal with respect to the pixel to be interpolated respectively, and calculates the plurality of second interpolated values respectively by the interpolation employing the plurality of pixels located in the plurality of directions about the direction indicated by the input signal with respect to the pixel to be interpolated respectively. The scanning line interpolation equipment determines the minimum value among the plurality of difference values, for selecting the second interpolated value corresponding to the difference value determined as the minimum value from the plurality of second interpolated values and supplying the same to the interpolated value output device.
Thus, false detection of the angle of the image can be corrected by determining the direction having the highest correlation among the plurality of directions and selecting the second interpolated value in the direction having the highest correlation from the second interpolated values of the plurality of directions.
The scanning line interpolation equipment may further comprise a detection device that detects the values of pixels vertically located above and under the pixel to be interpolated respectively and an intermediate value determination device that determines whether or not the second interpolated value calculated by the second interpolation device is between the values detected by the detection device, and the interpolated value output device may output the first interpolated value calculated by the first interpolation device as the value of the pixel to be interpolated regardless of the difference value calculated by the difference calculation device when the intermediate value determination device determines that the second interpolated value is not between the values detected by the detection device.
In this case, the scanning line interpolation equipment detects the values of the pixels vertically located above and under the pixel to be interpolated respectively and determines whether or not the second interpolated value is between the detected values. When determining that the second interpolated value is not between the detected values, the scanning line interpolation equipment outputs the first interpolated value as the value of the pixel to be detected regardless of the oblique difference value.
Thus, the scanning line interpolation equipment can be prevented from calculating the value of the pixel to be interpolated with pixels of a false direction when falsely detecting the angle of the image, by employing not the second interpolated value but the first interpolated value if the second interpolated value is not between the pixels located above and under the pixel to be interpolated.
The scanning line interpolation equipment may further comprise a vertical difference operation device that calculates the difference value between pixels vertically located above and under the pixel to be interpolated, and the interpolated value output device may output the first interpolated value calculated by the first interpolation device regardless of the difference value calculated by the difference calculation device when the difference value calculated by the vertical difference operation device is less than a predetermined value.
In this case, the scanning line interpolation equipment calculates the difference value between the pixels vertically located above and under the pixel to be interpolated, and outputs the first interpolated value as the value of the pixel to be interpolated regardless of the oblique difference value when the vertical difference value is less than the predetermined value.
Thus, picture quality can be prevented from deterioration resulting from false detection of the angle of the image by employing not the second interpolated value but the first interpolated value when the vertical difference value is smaller than the predetermined value.
The second interpolation device may average the pixels of the upper and lower scanning lines located in the direction indicated by the signal received in the input terminal with respect to the pixel to be interpolated as the second interpolated value.
In this case, the second interpolated value is defined by the average of the values of pixels obliquely located with respect to the pixel to be interpolated.
The first value may be zero, and the second value may be a preset threshold.
In this case, the scanning line interpolation equipment outputs the second interpolated value as the value of the pixel to be interpolated when the difference value is zero, outputs the first interpolated value as the value of the pixel to be interpolated when the difference value is in excess of the threshold, and outputs the third interpolated value calculated by the operation employing the first and second interpolated values as the value of the pixel to be interpolated when the difference value is within the range between zero and the threshold.
The scanning line interpolation equipment may further comprise an image angle detection device that detects an image angle related to the pixel to be interpolated on the basis of the input video signal and supplies the signal indicating the direction of the image to the input terminal, and the image angle detection device may include a binarized pattern generation device that binarizes the input video signal in a predetermined detection area including a plurality of scanning lines and the pixel to be interpolated and generates a binarized pattern, a reference pattern generation device that generates a binary image having a plurality of directions as a plurality of reference patterns and a comparison device that compares the binarized pattern generated by the binarized pattern generation device with each of the plurality of reference patterns generated by the reference pattern generation device and detects the image angle related to the pixel to be interpolated on the basis of the result of comparison.
In the image angle detection device, the binarized pattern generation device binarizes the input video signal in the predetermined detection area and generates the binarized pattern. The reference pattern generation device generates the binarized image having the plurality of directions as the plurality reference patterns. The comparison device compares the binarized pattern with each of the plurality of reference patterns and detects the image angle related to the pixel to be interpolated on the basis of the result of comparison.
In this case, false detection is suppressed as compared with a case of employing the difference value between two pixels due to comparison of two-dimensional patterns, whereby the angle of an image having an oblique edge can be correctly detected.
When employing two-dimensional reference patterns, detected angles are not restricted to the angle of a straight line connecting pixels located on point-symmetrical positions about the pixel to be interpolated but angles therebetween can also be detected. Therefore, the angles can be detected at smaller intervals without increasing the circuit scale.
The scanning line interpolation equipment may further comprise an image angle detection device that detects an image angle related to the pixel to be interpolated on the basis of the input video signal and supplies the signal indicating the direction of the image to the input terminal, and the image angle detection device may include a maximal/minimal pattern generation device that generates a maximal/minimal pattern indicating the position of the maximal point or the minimal point of horizontal luminance distribution every scanning line in a predetermined detection area including a plurality of scanning lines and the pixel to be interpolated in the input video signal, a reference pattern generation device that generates a plurality of reference patterns indicating the positions of the maximal points or the minimal points of horizontal luminance distribution every scanning line in the detection area and a comparison device compares the maximal/minimal pattern generated by the maximal/minimal pattern generation device with each of the plurality of reference patterns generated by the reference pattern generation device and detects the image angle related to the pixel to be interpolated on the basis of the result of comparison.
In the image angle detection device, the maximal/minimal pattern generation device generates the maximal/minimal pattern indicating the position of the maximal point or the minimal point of the horizontal luminance distribution every scanning line in the predetermined detection area in the input video signal. The reference pattern generation device generates the plurality of reference patterns indicating the positions of the maximal points or the minimal points of the horizontal luminance distribution every scanning line in the detection area. The comparison device compares the maximal/minimal pattern with each of the plurality of reference patterns, and detects the image angle related to the pixel to be interpolated on the basis of the result of comparison.
In this case, false detection is suppressed as compared with a case of employing the difference value between two pixels due to comparison of two-dimensional patterns, and the angle of an image having thin oblique lines can be correctly detected.
When employing two-dimensional reference patterns, detected angles are not restricted to the angle of a straight line connecting pixels located on point-symmetrical positions about the pixel to be interpolated but angles therebetween can also be detected. Therefore, the angles can be detected at smaller intervals without increasing the circuit scale.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.